* {
  padding: 0;
  margin: 0;
}
li {
  list-style: none;
}
.header {
  width: 600px;
  height: 300px;
  margin: 0 auto;
  background-color: skyblue;
  .nav {
    display: flex;
    .active{
        background-color: steelblue;
    }
    h3 {
      width: 200px;
      line-height: 60px;
      text-align:center;
    }
  }
  ul.active{
    display: block;
  }
  ul{
    margin-top: 20px;
    display: none;
    li{
        height: 30px;
        line-height: 30px;
    }
    button{
      margin-top: 4px;
      width: 80px;
      height: 30px;
      line-height: 30px;
      text-align: center;
    }
  }
}
